This invention relates to a gas cylinder for holding a gas under pressure, and specifically to a gas cylinder and method of fabricating a gas cylinder having a single leak point.
Typically, gas cylinders are used to store a pressurized gas such as carbon dioxide for use with recreational paintball guns or to store a propellant gas for non-pressurized fire extinguishers. A slow leak in a gas cylinder containing propellant renders the fire extinguisher, paintball gun or other device in operable. It is therefore desirable to use a substantially leak proof gas cylinder.
A gas cylinder for the above applications ideally holds a pressurized gas for extend periods of time through a wide range of environmental conditions. Conventional, gas cylinders are fabricated from a tubular member with open ends. Each of the open ends are closed by attaching a cap or plug. Another method of closing the cylinder is a hot spinning process. The hot spinning process includes spinning the sides of the cylinder at one end into each other to form a seal. The sidewalls of the tubular member are driven towards each other under heat and pressure to close and seal off the cylinder end.
Typically, the hot spinning process results in the ends of the cylinder including a greater wall thickness than that of the sides of the cylinder. Gas cylinders fabricated by the hot spinning method typically include three leak points. The first and second of these leak points are disposed at the ends of the gas cylinder formed from the hot spinning process. Leaks form in the ends because the joint or seal is composed of the joining of two members, which forms a seam or leak path. To prevent leaks at the hot spun ends of the gas cylinder, the ends are fabricated with an increased thickness by folding layer upon layer of tubular member onto itself. In some cases a leak path forms within the seam at the end of the cylinder.
A third leak point is formed at the gas inlet fitting of the gas cylinder. Typically, threads are formed in the walls of the gas cylinder and a valve assembly is threaded onto the gas cylinder. Leaks can form around the valve assembly through the threaded interface.
Disadvantageously, current methods of forming gas cylinders contribute to the formation of the leak points other than through the valve assembly for controlling flow of gas from the cylinder. Accordingly, it is desirable to design a gas cylinder having only one potential leak path.
The present invention is a gas cylinder assembly and method of fabricating a gas cylinder having a substantially uniform wall thickness and a single potential leak point.
The gas cylinder is fabricating by a deep drawing process. The deep drawing process utilizes a single sheet of material having a uniform thickness to form a cylinder having a single open end and walls of a substantially consistent thickness. The use of one uniform sheet of material eliminates potential leak paths through the cylinder wall.
The end of the cylinder includes an adapter for an inlet. Leakage around adapter is prevented by assembling the adapter to the cylinder with interference fit threads that prevent leakage through the threads. The interference fit between the threads of the adapter and the cylinder prevent the adapter from being assembled with both the cylinder and adapter at a common temperature. The temperature of the adapter is elevated above that of the gas cylinder to expand the adapter to a size allowing assembly to the cylinder. The adapter is then cooled to the same temperature as the cylinder. The interference fit forms a leak proof seal that cannot be removed.
Accordingly, the gas cylinder of this invention provides a cylinder having only a single potential leak path through the inlet.